Grain Boundary Deformation-Induced Intergranular Stress Corrosion Cracking of Ni-16Cr-9Fe in 360°C Water

The objective of this research was to determine whether grain boundary deformation plays a direct role in intergranular stress corrosion cracking (IGSCC) of Ni-16Cr-9Fe in high-temperature water. The difference in deformation and cracking behavior between special grain boundaries, or coincident site lattice boundaries (CLSB), and high-angle boundaries (HAB) was exploited to determine if a cause-and-effect relationship exists between grain boundary deformation and IGSCC. At high temperature, extrinsic grain boundary dislocations (EGBD) were observed to annihilate at HAB at a higher rate than at CSLB (by a factor of 3). After 10% strain in 360°C argon, 53% of HAB were observed to undergo deformation as compared to only 18% of CSLB. To determine whether grain boundary deformation and IGSCC are related, samples deformed 10% in argon were then given a 5% strain in 360°C primary water. Resulting analysis showed that 61% of the boundaries that deformed in argon also cracked in water, while only 17% of cracked boundaries showed no prior deformation in argon. These results establish that there is a cause-and-effect relationship between grain boundary deformation and IGSCC.